Shale hydration inhibition agent and method of use

ABSTRACT

A water-base fluid for use in drilling, cementing, workover, fracturing and abandonment of subterranean wells through a formation containing a shale which swells in the presence of water. In one illustrative embodiment, the drilling fluid includes, an aqueous based continuous phase, a weighting agent, and a shale hydration inhibition agent. The shale hydration inhibition agent should have the general formula: 
     
       
         
         
             
             
         
       
     
     in which A is independently selected from H and CH 2 CH 2 CH 2 NH 2 ; and in which B is independently selected from H, CH 2 CH 2 OH, CH 2 CH 2 OCH 2 CH 2 CH 2 NH 2  and CH 2 CH 2 CH 2 NH 2 . The shale hydration inhibition agent is present in sufficient concentration to substantially reduce the swelling of shale drilling cuttings upon contact with the drilling fluid. The drilling fluid may be formulated to include a wide variety of components of aqueous based drilling fluids, such as weighting agents, fluid loss control agents, suspending agents, viscosifying agents, rheology control agents, as well as other compounds and materials known to one of skill in the art. The fluids may also be used in the disposal by reinjection of drilling cutting into a selected subterranean disposal formation.

BACKGROUND

In rotary drilling of subterranean wells numerous functions andcharacteristics are expected of a drilling fluid. A drilling fluidshould circulate throughout the well and carry cuttings from beneath thebit, transport the cuttings up the annulus, and allow their separationat the surface. At the same time, the drilling fluid is expected to cooland clean the drill bit, reduce friction between the drill string andthe sides of the hole, and maintain stability in the borehole's uncasedsections. The drilling fluid should also form a thin, low permeabilityfilter cake that seals openings in formations penetrated by the bit andact to reduce the unwanted influx of formation fluids from permeablerocks.

Drilling fluids are typically classified according to their basematerial. In oil base fluids, solid particles are suspended in oil, andwater or brine may be emulsified with the oil. The oil is typically thecontinuous phase. In water base fluids, solid particles are suspended inwater or brine, and oil may be emulsified in the water. The water istypically the continuous phase. Pneumatic fluids are a third class ofdrilling fluids in which a high velocity stream of air or natural gasremoves drill cuttings.

Three types of solids are usually found in water base drillingfluids: 1) clays and organic colloids added to provide necessaryviscosity and filtration properties; 2) heavy minerals whose function isto increase the drilling fluid's density; and 3) formation solids thatbecome dispersed in the drilling fluid during the drilling operation.

The formation solids that become dispersed in a drilling fluid aretypically the cuttings produced by the drill bit's action and the solidsproduced by borehole instability. Where the formation solids are clayminerals that swell, the presence of either type of formation solids inthe drilling fluid can greatly increase drilling time and costs.

Clay minerals are generally crystalline in nature. The structure of aclay's crystals determines its properties. Typically, clays have aflaky, mica-type structure. Clay flakes are made up of a number ofcrystal platelets stacked face-to-face. Each platelet is called a unitlayer, and the surfaces of the unit layer are called basal surfaces.

A unit layer is composed of multiple sheets. One sheet is called theoctahedral sheet, it is composed of either aluminum or magnesium atomsoctahedrally coordinated with the oxygen atoms of hydroxyls. Anothersheet is called the tetrahedral sheet. The tetrahedral sheet consists ofsilicon atoms tetrahedrally coordinated with oxygen atoms.

Sheets within a unit layer link together by sharing oxygen atoms. Whenthis linking occurs between one octahedral and one tetrahedral sheet,one basal surface consists of exposed oxygen atoms while the other basalsurface has exposed hydroxyls. It is also quite common for twotetrahedral sheets to bond with one octahedral sheet by sharing oxygenatoms. The resulting structure, known as the Hoffman structure, has anoctahedral sheet that is sandwiched between the two tetrahedral sheets.As a result, both basal surfaces in a Hoffman structure are composed ofexposed oxygen atoms.

The unit layers stack together face-to-face and are held in place byweak attractive forces. The distance between corresponding planes inadjacent unit layers is called the c-spacing. A clay crystal structurewith a unit layer consisting of three sheets typically has a c-spacingof about 9.5×10⁻⁷ mm.

In clay mineral crystals, atoms having different valences commonly willbe positioned within the sheets of the structure to create a negativepotential at the crystal surface. In that case, a cation is adsorbed onthe surface. These adsorbed cations are called exchangeable cationsbecause they may chemically trade places with other cations when theclay crystal is suspended in water. In addition, ions may also beadsorbed on the clay crystal edges and exchange with other ions in thewater.

The type of substitutions occurring within the clay crystal structureand the exchangeable cations adsorbed on the crystal surface greatlyaffect clay swelling, a property of primary importance in the drillingfluid industry. Clay swelling is a phenomenon in which water moleculessurround a clay crystal structure and position themselves to increasethe structure's c-spacing thus resulting in an increase in volume. Twotypes of swelling may occur.

Surface hydration is one type of swelling in which water molecules areadsorbed on crystal surfaces. Hydrogen bonding holds a layer of watermolecules to the oxygen atoms exposed on the crystal surfaces.Subsequent layers of water molecules align to form a quasi-crystallinestructure between unit layers, which results in an increased c-spacing.Virtually all types of clays swell in this manner.

Osmotic swelling is a second type of swelling. Where the concentrationof cations between unit layers in a clay mineral is higher than thecation concentration in the surrounding water, water is osmoticallydrawn between the unit layers and the c-spacing is increased. Osmoticswelling results in larger overall volume increases than surfacehydration. However, only certain clays, like sodium montmorillonite,swell in this manner.

Exchangeable cations found in clay minerals are reported to have asignificant impact on the amount of swelling that takes place. Theexchangeable cations compete with water molecules for the availablereactive sites in the clay structure. Generally cations with highvalences are more strongly adsorbed than ones with low valences. Thus,clays with low valence exchangeable cations will swell more than clayswhose exchangeable cations have high valences.

In the North Sea and the United States Gulf Coast, drillers commonlyencounter argillaceous sediments in which the predominant clay mineralis sodium montmorillonite (commonly called “gumbo shale”). Sodiumcations are predominately the exchangeable cations in gumbo shale. Asthe sodium cation has a low positive valence (i.e. formally a +1valence), it easily disperses into water. Consequently, gumbo shale isnotorious for its swelling.

Clay swelling during the drilling of a subterranean well can have atremendous adverse impact on drilling operations. The overall increasein bulk volume accompanying clay swelling impedes removal of cuttingsfrom beneath the drill bit, increases friction between the drill stringand the sides of the borehole, and inhibits formation of the thin filtercake that seals formations. Clay swelling can also create other drillingproblems such as loss of circulation or stuck pipe that slow drillingand increase drilling costs. Thus, given the frequency in which gumboshale is encountered in drilling subterranean wells, the development ofa substance and method for reducing clay swelling remains a continuingchallenge in the oil and gas exploration industry.

One method to reduce clay swelling is to use salts in drilling fluids.Salts generally reduce the swelling of clays. However, salts flocculatethe clays resulting in both high fluid losses and an almost completeloss of thixotropy. Further, increasing salinity often decreases thefunctional characteristics of drilling fluid additives.

Another method for controlling clay swelling is to use organic shaleinhibitor molecules in drilling fluids. It is believed that the organicshale inhibitor molecules are adsorbed on the surfaces of clays with theadded organic shale inhibitor competing with water molecules for clayreactive sites and thus serve to reduce clay swelling.

It is important that the driller of subterranean wells be able tocontrol the rheological properties of drilling fluids by usingadditives, including organic shale inhibitor molecules. In the oil andgas industry today it is desirable that additives work both onshore andoffshore and in fresh and salt water environments. In addition, asdrilling operations impact on plant and animal life, drilling fluidadditives should have low toxicity levels and should be easy to handleand to use to minimize the dangers of environmental pollution and harmto operators. Any drilling fluid additive should also provide desirableresults but should not inhibit the desired performance of otheradditives. The development of such additives will help the oil and gasindustry to satisfy the long felt need for superior drilling fluidadditives which act to control the swelling of the clay and drilledformations without adversely effecting the rheological properties ofdrilling fluids. The claimed subject matter addresses this need.

SUMMARY

Upon consideration of the present disclosure, one of skill in the artshould understand and appreciate that one illustrative embodiment of theclaimed subject matter includes a water-base drilling fluid for use indrilling wells through a formation containing a shale which swells inthe presence of water. In such an illustrative embodiment, the drillingfluid includes, an aqueous based continuous phase, a weighting agent,and a shale hydration inhibition agent. The shale hydration inhibitionagent should have the general formula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. The shale hydration inhibition agent is present insufficient concentration to substantially reduce the swelling of shaledrilling cuttings upon contact with the drilling fluid. As noted above,the illustrative shale hydration inhibition agent is preferably thereaction product of a hydrogenation reaction of the product of thereaction of triethanolamine and acrylonitrile. Alternatively the shalehydration inhibition agent may be the reaction product of ahydrogenation reaction of the product of the reaction of diethanolamineand acrylonitrile. In a particularly preferred illustrative embodiment,the shale hydration inhibition agent is selected from:

as well as mixtures of these. The illustrative drilling fluid isformulated such that the aqueous based continuous phase is selectedfrom: fresh water, sea water, brine, mixtures of water and water solubleorganic compounds as well as mixtures and combinations of these andsimilar aqueous based fluids that should be known to one of skill in theart. In one illustrative embodiment, an optional viscosifying agent isincluded in the drilling fluid and the viscosifying agent is preferablyselected from mixtures and combinations of compounds that should beknown to one of skill in the art such as xanthan gums, starches,modified starches and synthetic viscosifiers such as polyarcylamides,and the like. A weighting material such as barite, calcite, hematite,iron oxide, calcium carbonate, organic and inorganic salts, as well asmixtures and combinations of these and similar compounds that should beknown to one of skill in the art may also be included into theformulation of the illustrative fluid. The illustrative fluid may alsoinclude a wide variety of conventional components of aqueous baseddrilling fluids, such as fluid loss control agents, suspending agents,viscosifying agents, rheology control agents, as well as other compoundsand materials that one of skill in the art would be knowledgeable about.

The scope of the claimed subject matter also encompasses a fracturingfluid for use in a subterranean well in which the subterranean wellpenetrates through one or more subterranean formation composed of ashale that swells in the presence of water. One illustrative fluid isformulated to include an aqueous based continuous phase, a viscosifyingagent and a shale hydration inhibition agent which is present insufficient concentration to substantially reduce the swelling of shale.In one illustrative embodiment, the shale hydration inhibition agent hasthe formula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. Alternatively, the shale hydration inhibition agent ofthe illustrative fluid may be selected from

as well as mixtures of these. As noted above, the illustrative shalehydration inhibition agent is preferably the reaction product of ahydrogenation reaction of the product of the reaction of triethanolamineand acrylonitrile. Alternatively the shale hydration inhibition agentmay be the reaction product of a hydrogenation reaction of the productof the reaction of diethanolamine and acrylonitrile. The illustrativefluid is formulated such that the aqueous based continuous phase may beselected from: fresh water, sea water, brine, mixtures of water andwater soluble organic compounds as well as mixtures and combinations ofthese and similar aqueous based fluids that should be known to one ofskill in the art. In one illustrative embodiment, an optionalviscosifying agent is included in the drilling fluid and theviscosifying agent is preferably selected mixtures and combinations ofcompounds that should be known to one of skill in the art such asxanthan gums, starches, modified starches and synthetic viscosifierssuch as polyarcylamides, and the like. A weighting material such asbarite, calcite, hematite, iron oxide, calcium carbonate, organic andinorganic salts, as well as mixtures and combinations of these andsimilar compounds that should be known to one of skill in the art mayalso be included into the formulation of the illustrative fluid. Theillustrative fluid may also include a wide variety of conventionalcomponents of fracturing fluids, such as propants such as sand, gravel,glass beads, ceramic materials and the like, acid release agents, fluidloss control agents, suspending agents, viscosifying agents, rheologycontrol agents, as well as other compounds and materials that one ofskill in the art would be knowledgeable about.

It should also be appreciated that the claimed subject matter inherentlyincludes components such as: an aqueous based continuous phase; aswellable shale material; and a shale hydration inhibition agent presentin sufficient concentration to substantially reduce the swelling of theswellable shale material. Such a composition may be formed during thecourse of drilling a subterranean well, but also may be deliberatelymade if drill cuttings reinjection is to be carried out. In oneillustrative embodiment, the shale hydration inhibition agent has theformula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. Alternatively, the shale hydration inhibition agent ofthe illustrative composition may be selected from

as well as mixtures of these. As noted above, the illustrative shalehydration inhibition agent is preferably the reaction product of ahydrogenation reaction of the product of the reaction of triethanolamineand acrylonitrile. Alternatively the shale hydration inhibition agentmay be the reaction product of a hydrogenation reaction of the productof the reaction of diethanolamine and acrylonitrile. The illustrativecomposition is formulated such that the aqueous based continuous phasemay be selected from: fresh water, sea water, brine, mixtures of waterand water soluble organic compounds as well as mixtures and combinationsof these and similar aqueous based fluids that should be known to one ofskill in the art. In one illustrative embodiment, an optionalviscosifying agent is included in the drilling fluid and theviscosifying agent is preferably selected mixtures and combinations ofcompounds that should be known to one of skill in the art such asxanthan gums, starches, modified starches and synthetic viscosifierssuch as polyarcylamides, and the like. A weighting material such asbarite, calcite, hematite, iron oxide, calcium carbonate, organic andinorganic salts, as well as mixtures and combinations of these andsimilar compounds that should be known to one of skill in the art mayalso be included into the formulation of the illustrative composition.The illustrative composition may also include a wide variety ofconventional components of drilling and well bore fluids, such as fluidloss control agents, suspending agents, viscosifying agents, rheologycontrol agents, as well as other compounds and materials that one ofskill in the art would be knowledgeable about.

One of skill in the art should appreciate that the fluids of the claimedsubject matter are useful during the course of the drilling, cementing,fracturing, maintenance and production, workover, abandonment a well asother operations associated with subterranean wells. The claimed subjectmatter also includes a method of disposing of drill cuttings into asubterranean formation. It should also be appreciated by one of skill inthe art that the claimed subject matter inherently includes a method ofreducing the swelling of shale clay in a well, the method includingcirculating in the well a water-base drilling fluid formulated as issubstantially disclosed herein. These and other features of the claimedsubject matter are more fully set forth in the following description ofillustrative embodiments of the claimed subject matter.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The claimed subject matter is directed to a water-base drilling fluidfor use in drilling wells through a formation containing a shale whichswells in the presence of water. Generally the drilling fluid of theclaimed subject matter may be formulated to include an aqueouscontinuous phase and a shale hydration inhibition agent. As disclosedbelow, the drilling fluids of the claimed subject matter may optionallyinclude additional components, such as weighting agents, viscosityagents, fluid loss control agents, bridging agents, lubricants, anti-bitballing agents, corrosion inhibition agents, alkali reserve materialsand buffering agents, surfactants and suspending agents, rate ofpenetration enhancing agents and the like that one of skill in the artshould understand may be added to an aqueous based drilling fluid.

The aqueous based continuous phase may generally be any water basedfluid phase that is compatible with the formulation of a drilling fluidand is compatible with the shale hydration inhibition agents disclosedherein. In one preferred embodiment, the aqueous based continuous phaseis selected from: fresh water, sea water, brine, mixtures of water andwater soluble organic compounds and mixtures thereof. The amount of theaqueous based continuous phase should be sufficient to form a waterbased drilling fluid. This amount may range from nearly 100% of thedrilling fluid to less than 30% of the drilling fluid by volume.Preferably, the aqueous based continuous phase is from about 95 to about30% by volume and preferably from about 90 to about 40% by volume of thedrilling fluid.

A shale hydration inhibition agent is included in the formulation of thedrilling fluids of the claimed subject matter so that the hydration ofshale and shale like formations is inhibited. Thus, the shale hydrationinhibition agent should be present in sufficient concentration to reduceeither or both the surface hydration based swelling and/or the osmoticbased swelling of the shale clay. The exact amount of the shalehydration inhibition agent present in a particular drilling fluidformulation can be determined by a trial and error method of testing thecombination of drilling fluid and shale clay formation encountered.Generally however, the shale hydration inhibition agent of the claimedsubject matter may be used in drilling fluids in a concentration fromabout 1 to about 18 pounds per barrel (lbs/bbl or ppb) and morepreferably in a concentration from about 2 to about 12 pounds per barrelof drilling fluid.

The shale hydration inhibition agent of the claimed subject mattershould have the general formula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. The shale hydration inhibition agent is present insufficient concentration to substantially reduce the swelling of shaledrilling cuttings upon contact with the drilling fluid. In aparticularly preferred illustrative embodiment, the shale hydrationinhibition agent is selected from:

as well as mixtures of these.

When considering the illustrative shale hydration inhibition agentsdisclosed above, one skilled in organic synthesis should recognize thata wide variety of synthetic reaction pathways can be used to reach theabove target molecules. It has been found that one desirable andeconomic way to achieve the target compounds is the reaction oftriethanolamine and acrylonitrile followed by hydrogenation of theresulting reaction product. Alternatively the shale hydration inhibitionagent may be the reaction product of a hydrogenation reaction of aproduct of the reaction of diethanolamine and acrylonitrile. Thetechniques, required apparatus, and reaction conditions for carrying outsuch reactions should be easily obtained from the appropriate literatureby one of skill in the art of organic synthesis. In some instances theabove compounds may be commercially available from specialty chemicalsuppliers although their use and application may be in a field otherthan drilling fluid formulation.

The drilling fluids of the claimed subject matter can include a weightmaterial in order to increase the density of the fluid. The primarypurpose for such weighting materials is to increase the density of thedrilling fluid so as to prevent kick-backs and blow-outs. One of skillin the art should know and understand that the prevention of kick-backsand blow-outs is important to the safe day to day operations of adrilling rig. Thus the weight material is added to the drilling fluid ina functionally effective amount largely dependent on the nature of theformation being drilled. Weight materials suitable for use in theformulation of the drilling fluids of the claimed subject matter may begenerally selected from any type of weighting materials be it in solid,particulate form, suspended in solution, dissolved in the aqueous phaseas part of the preparation process or added afterward during drilling.It is preferred that the weight material be selected from the groupincluding barite, hematite, iron oxide, calcium carbonate, magnesiumcarbonate, organic and inorganic salts, and mixtures and combinations ofthese compounds and similar such weight materials that may be utilizedin the formulation of drilling fluids.

The drilling fluids of the claimed subject matter can include aviscosifying agent in order to alter or maintain the Theologicalproperties of the fluid. The primary purpose for such viscosifyingagents is to control the viscosity and potential changes in viscosity ofthe drilling fluid. Viscosity control is particularly important becauseoften a subterranean formation may have a temperature significantlyhigher than the surface temperature. Thus a drilling fluid may undergotemperature extremes of nearly freezing temperatures to nearly theboiling temperature of water or higher during the course of its transitfrom the surface to the drill bit and back. One of skill in the artshould know and understand that such changes in temperature can resultin significant changes in the rheological properties of fluids. Thus inorder to control and/or moderate the rheology changes, viscosity agentsand rheology control agents may be included in the formulation of thedrilling fluid. Viscosifying agents suitable for use in the formulationof the drilling fluids of the claimed subject matter may be generallyselected from any type of viscosifying agents suitable for use inaqueous based drilling fluids. In one illustrative embodiment, anoptional viscosifying agent is included in the drilling fluid and theviscosifying agent is preferably selected mixtures and combinations ofcompounds that should be known to one of skill in the art such asxanthan gums, starches, modified starches and synthetic viscosifierssuch as polyarcylamides, and the like.

In addition to the components noted above, the claimed drilling fluidsmay also be formulated to include materials generically referred to asalkali reserve and alkali buffering agent, gelling materials, thinners,and fluid loss control agents, as well as other compounds and materialswhich are optionally added to water base drilling fluid formulations. Ofthese additional materials, each can be added to the formulation in aconcentration as rheologically and functionally required by drillingconditions.

One of skill in the art should appreciate that lime is the principlealkali reserve agent utilized in formulating water based drillingfluids. Alkali buffering agents, such as cyclic organic amines,sterically hindered amines, amides of fatty acids and the like may alsobe included to serve as a buffer against the loss of the alkali reserveagent. The drilling fluid may also contain anticorrosion agents as wellto prevent corrosion of the metal components of the drilling operationalequipment. Gelling materials are also often used in aqueous baseddrilling fluids and these include bentonite, sepiolite, clay,attapulgite clay, anionic high-molecular weight polymers andbiopolymers. Thinners such as lignosulfonates are also often added towater-base drilling fluids. Typically lignosulfonates, modifiedlignosulfonates, polyphosphates and tannins are added. In otherembodiments, low molecular weight polyacrylates can also be added asthinners. Thinners are added to a drilling fluid to reduce flowresistance and control gelation tendencies. Other functions performed bythinners include reducing filtration and filter cake thickness,counteracting the effects of salts, minimizing the effects of water onthe formations drilled, emulsifying oil in water, and stabilizing mudproperties at elevated temperatures.

A variety of fluid loss control agents may be added to the drillingfluids of the claimed subject matter that are generally selected from agroup consisting of synthetic organic polymers, biopolymers, andmixtures thereof The fluid loss control agents such as modified lignite,polymers, modified starches and modified celluloses may also be added tothe water base drilling fluid system of this invention. In oneembodiment it is preferred that the additives of the invention should beselected to have low toxicity and to be compatible with common anionicdrilling fluid additives such as polyanionic carboxymethylcellulose (PACor CMC), polyacrylates, partially-hydrolyzed polyacrylamides (PHPA),lignosulfonates, xanthan gum, mixtures of these and the like.

The drilling fluid of the claimed subject matter may further contain anencapsulating agent generally selected from the group consisting ofsynthetic organic, inorganic and bio-polymers and mixtures thereof. Therole of the encapsulating agent is to absorb at multiple points alongthe chain onto the clay particles, thus binding the particles togetherand encapsulating the cuttings. These encapsulating agents help improvethe removal of cuttings with less dispersion of the cuttings into thedrilling fluids. The encapsulating agents may be anionic, cationic,amphoteric, or non-ionic in nature.

Other additives that could be present in the drilling fluids of theclaimed subject matter include products such as lubricants, penetrationrate enhancers, defoamers, fluid loss circulation products and so forth.Such compounds should be known to one of ordinary skill in the art offormulating aqueous based drilling fluids.

The following-examples are included to demonstrate preferred embodimentsof the claimed subject matter. It should be appreciated by those ofskill in the art that the techniques disclosed in the examples whichfollow represent techniques discovered by the inventors to function wellin the practice of the claimed subject matter, and thus can beconsidered to constitute preferred modes for its practice. However,those of skill in the art should, in light of the present disclosure,appreciate that many changes can be made in the specific embodimentswhich are disclosed and still obtain a like or similar result withoutdeparting from the scope of the claimed subject matter.

Unless otherwise stated, all starting materials are commerciallyavailable and standard laboratory techniques and equipment are utilized.The tests were conducted in accordance with the procedures in APIBulletin RP 13B-2, 1990. The following abbreviations are sometimes usedin describing the results discussed in the examples:

-   -   “PV” is plastic viscosity (CPS) which is one variable used in        the calculation of viscosity characteristics of a drilling        fluid.    -   “YP” is yield point (lbs/100 ft²)which is another variable used        in the calculation of viscosity characteristics of drilling        fluids.    -   “GELS” (lbs/100 ft²)is a measure of the suspending        characteristics and the thixotropic properties of a drilling        fluid.    -   “F/L” is API fluid loss and is a measure of fluid loss in        milliliters of drilling fluid at 100 psi.

EXAMPLE 1

The following drilling muds are formulated to illustrate the claimedsubject matter:

A B C Fresh Water 259.45 ppb 259.45 ppb 259.45 ppb Sea Salt 11.09 ppb11.09 ppb 11.09 ppb Technical grade 66.01 ppb 66.01 ppb 66.01 ppb sodiumchloride (Driller's salt) UltraCap 2.0 ppb 2.0 ppb 2.0 ppb UltraFree10.5 ppb 10.5 ppb 10.5 ppb PolyPac 2.0 ppb 2.0 ppb 2.0 ppb DuoVis 0.75ppb 0.75 ppb 0.75 ppb Rev Dust 25.0 ppb 25.0 ppb 25.0 ppb Barite 123.18ppb 123.18 ppb 123.18 ppb RMR 13-21A 10.5 ppb RMR 13-21B 10.5 ppb RMR13-35 10.5 ppb

In the above mud formulation the following commercially availablecompounds have been used in the formulation of the drilling fluid, butone of skill in the art should appreciate that other similar compoundsmay be used instead.

UltraCap Cationic polyacrylamide availale from M-I LLC. UltraFreeMixutre of surfactants and lubricants available from M-I LLC PolyPacPoly anionic cellulose DuoVis Natural polymeric viscosifier, such asxanthan gum, starches.

In the above mud formulation the following shale inhibitors areutilized: RMR 13–21A is a triethanolaminetriamine having the formula

and which is commercially available form Champion Chemicals.

RMR 13–21B is a diethanolaminediamine having the formula

and which is commercially available from Champion Chemicals

RMR 13–35 is a triethanolamine diamine having the formula

and which is commercially available from Champion Chemical.

The properties of the above muds as well as a base mud (i.e. a mud inwhich there is no shale inhibitor) are measured and give the followingexemplary data:

Properties Base Mud A B C Viscosity (cps) at 600 rpm 81 101 98 101 300rpm 51 62 59 65 200 rpm 39 48 46 50 100 rpm 26 33 30 33  6 rpm 7 9 8 10 3 rpm 5 9 6 8 Gels 10 sec. 7 11 7 9 10 min. 7 13 9 12 PV 30 39 39 36 YP21 23 20 29 F/L 7.8 6.4 5.4 5.2

Dispersion tests are run with Arne Clay cuttings by hot rolling 10 g ofcuttings in a one-barrel equivalent of mud for 16 hours at 150° F. Afterhot rolling the remaining cuttings are screened using a 20 mesh screenand washed with 10% potassium chloride water, dried and weighed toobtain the percentage recovered. The results of this evaluation aregiven in the following Table and shows the improved shale inhibitionperformance of shale inhibition agents of this invention.

(% cuttings recovered) Base Mud A B Arne 76.7 88.0 88.6

To further demonstrate the performance of the drilling fluids formulatedin accordance with the teachings of this invention, a test using a bulkhardness tester is conducted. A BP Bulk Hardness Tester is a devicedesigned to give an assessment of the hardness of shale cuttings exposedto drilling fluids, which in turn can be related to the inhibitingproperties of the drilling fluid being evaluated. In this test, shalecuttings are hot rolled in the test drilling fluid at 150° F. for 16hours. Shale cuttings are screened and then placed into a BP BulkHardness Tester. The equipment is closed and using a torque wrench theforce used to extrude the cuttings through a plate with holes in it isrecorded. Depending on the hydration state and hardness of the cuttingsand the drilling fluid used, a plateau region in torque is reached asextrusion of the cuttings begins to take place. Alternatively, thetorque may continue to rise which tends to occur with harder cuttingsamples. Therefore, the higher the torque number obtained, the moreinhibitive the drilling fluid system is considered. Illustrative dataobtained using the three different mud formulations with two differentcuttings are given below.

Bulk Hardness: (values in inch/lbs) Arne Clay Mud Formulation Turn No.Base Mud A B C 8 — 15 15 10 9 10 40 40 50 10 15 130 130 80 11 20 170 170100 12 20 190 180 100 13 20 215 200 100 14 20 250 250 120 15 30 D/S D/S210 In the above table, D indicates formation of a disk; S indicates theformation of spaghetti like extrudates.

Foss Bulk Hardness: Eikeland (values in inch/lbs) Clay Mud FormulationTurn No. Base Mud A B C 8 — 10 10 10 9 — 30 25 30 10 15 185 160 200 1185 320 350 280 12 110 350 D/S 300 13 120 D/S 350 14 160 D/S In the abovetable, D indicates contact of the disk; S indicates the formation ofspaghetti like extrudates.

Upon review of the above data, one skilled in the art should observethat drilling fluids formulated according to the teachings of thisinvention prevent the hydration of various types of shale clays and thusare likely to provide good performance in drilling subterranean wellsencountering such shale clays.

In view of the above disclosure, one of skill in the art shouldunderstand and appreciate that one illustrative embodiment of theclaimed subject matter includes a water-base drilling fluid for use indrilling wells through a formation containing a shale which swells inthe presence of water. In such an illustrative embodiment, the drillingfluid includes, an aqueous based continuous phase, a weighting agent,and a shale hydration inhibition agent. The shale hydration inhibitionagent should have the general formula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. The shale hydration inhibition agent is present insufficient concentration to substantially reduce the swelling of shaledrilling cuttings upon contact with the drilling fluid. As noted above,the illustrative shale hydration inhibition agent is preferably thereaction product of a hydrogenation reaction of the product of thereaction of triethanolamine and acrylonitrile. Alternatively the shalehydration inhibition agent may be the reaction product of ahydrogenation reaction of the product of the reaction of diethanolamineand acrylonitrile. In a particularly preferred illustrative embodiment,the shale hydration inhibition agent is selected from:

as well as mixtures of these. The illustrative drilling fluid isformulated such that the aqueous based continuous phase is selectedfrom: fresh water, sea water, brine, mixtures of water and water solubleorganic compounds as well as mixtures and combinations of these andsimilar aqueous based fluids that should be known to one of skill in theart. In one illustrative embodiment, an optional viscosifying agent isincluded in the drilling fluid and the viscosifying agent is preferablyselected mixtures and combinations of compounds that should be known toone of skill in the art such as xanthan gums, starches, modifiedstarches and synthetic viscosifiers such as polyarcylamides, and thelike. A weighting material such as barite, calcite, hematite, ironoxide, calcium carbonate, organic and inorganic salts, as well asmixtures and combinations of these and similar compounds that should beknown to one of skill in the art may also be included into theformulation of the illustrative fluid. The illustrative fluid may alsoinclude a wide variety of conventional components of aqueous baseddrilling fluids, such as fluid loss control agents, suspending agents,viscosifying agents, rheology control agents, as well as other compoundsand materials that one of skill in the art would be knowledgeable about.

The scope of the claimed subject matter also encompasses a fracturingfluid for use in a subterranean well in which the subterranean wellpenetrates through one or more subterranean formations composed of ashale that swells in the presence of water. One illustrative fluid isformulated to include an aqueous based continuous phase, a viscosifyingagent and a shale hydration inhibition agent which is present insufficient concentration to substantially reduce the swelling of shale.In one illustrative embodiment, the shale hydration inhibition agent hasthe formula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. Alternatively, the shale hydration inhibition agent ofthe illustrative fluid may be selected from

as well as mixtures of these. As noted above, the illustrative shalehydration inhibition agent is preferably the reaction product of ahydrogenation reaction of the product of the reaction of triethanolamineand acrylonitrile. Alternatively the shale hydration inhibition agentmay be the reaction product of a hydrogenation reaction of the productof the reaction of diethanolamine and acrylonitrile. The illustrativefluid is formulated such that the aqueous based continuous phase may beselected from: fresh water, sea water, brine, mixtures of water andwater soluble organic compounds as well as mixtures and combinations ofthese and similar aqueous based fluids that should be known to one ofskill in the art. In one illustrative embodiment, an optionalviscosifying agent is included in the drilling fluid and theviscosifying agent is preferably selected mixtures and combinations ofcompounds that should be known to one of skill in the art such asxanthan gums, starches, modified starches and synthetic viscosifierssuch as polyarcylamides, and the like. A weighting material such asbarite, calcite, hematite, iron oxide, calcium carbonate, organic andinorganic salts, as well as mixtures and combinations of these andsimilar compounds that should be known to one of skill in the art mayalso be included into the formulation of the illustrative fluid. Theillustrative fluid may also include a wide variety of conventionalcomponents of fracturing fluids, such as propants such as sand, gravel,glass beads, ceramic materials and the like, acid release agents, fluidloss control agents, suspending agents, viscosifying agents, rheologycontrol agents, as well as other compounds and materials that one ofskill in the art would be knowledgeable about.

It should also be appreciated that the claimed subject matter inherentlyincludes a composition that includes: an aqueous based continuous phase;a swellable shale material; and a shale hydration inhibition agentpresent in sufficient concentration to substantially reduce the swellingof the swellable shale material. Such a composition may be formed duringthe course of drilling a subterranean well, but also may be deliberatelymade if drill cuttings reinjection is to be carried out. In oneillustrative embodiment, the shale hydration inhibition agent has theformula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂Alternatively, the shale hydration inhibition agent ofthe illustrative composition may be selected from

as well as mixtures of these. As noted above, the illustrative shalehydration inhibition agent is preferably the reaction product of ahydrogenation reaction of the product of the reaction of triethanolamineand acrylonitrile. Alternatively the shale hydration inhibition agentmay be the reaction product of a hydrogenation reaction of the productof the reaction of diethanolamine and acrylonitrile. The illustrativecomposition is formulated such that the aqueous based continuous phasemay be selected from: fresh water, sea water, brine, mixtures of waterand water soluble organic compounds as well as mixtures and combinationsof these and similar aqueous based fluids that should be known to one ofskill in the art. In one illustrative embodiment, an optionalviscosifying agent is included in the drilling fluid and theviscosifying agent is preferably selected mixtures and combinations ofcompounds that should be known to one of skill in the art such asxanthan gums, starches, modified starches and synthetic viscosifierssuch as polyarcylamides, and the like. A weighting material such asbarite, calcite, hematite, iron oxide, calcium carbonate, organic andinorganic salts, as well as mixtures and combinations of these andsimilar compounds that should be known to one of skill in the art mayalso be included into the formulation of the illustrative composition.The illustrative composition may also include a wide variety ofconventional components of drilling and well bore fluids, such as fluidloss control agents, suspending agents, viscosifying agents, rheologycontrol agents, as well as other compounds and materials that one ofskill in the art would be knowledgeable about.

One of skill in the art should appreciate that the fluids of the claimedsubject matter are useful during course of the drilling, cementing,fracturing, maintenance and production, workover, abandonment of a wellor other operations associated with subterranean wells. In oneillustrative embodiment, the fluids are utilized in a method involvingthe drilling a subterranean well through one or more subterraneanformations containing a shale which swells in the presence of water. Theillustrative method is carried out using conventional drilling means andtechniques, however, the drilling fluid utilized is formulated toinclude: an aqueous based continuous phase; a weighting agent; and ashale hydration inhibition agent present in sufficient concentration toreduce the swelling of shale. In one illustrative embodiment, the shalehydration inhibition agent has the formula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. Alternatively, the shale hydration inhibition agent ofthe illustrative composition may be selected from

as well as mixtures of these. As noted above, the illustrative shalehydration inhibition agent is preferably the reaction product of ahydrogenation reaction of the product of the reaction of triethanolamineand acrylonitrile. Alternatively the shale hydration inhibition agentmay be the reaction product of a hydrogenation reaction of the productof the reaction of diethanolamine and acrylonitrile. The illustrativedrilling fluid is formulated such that the aqueous based continuousphase may be selected from: fresh water, sea water, brine, mixtures ofwater and water soluble organic compounds as well as mixtures andcombinations of these and similar aqueous based fluids that should beknown to one of skill in the art. In one illustrative embodiment, anoptional viscosifying agent is included in the drilling fluid and theviscosifying agent is preferably selected mixtures and combinations ofcompounds that should be known to one of skill in the art such asxanthan gums, starches, modified starches and synthetic viscosifierssuch as polyarcylamides, and the like. A weighting material such asbarite, calcite, hematite, iron oxide, calcium carbonate, organic andinorganic salts, as well as mixtures and combinations of these andsimilar compounds that should be known to one of skill in the art mayalso be included into the formulation of the illustrative drillingfluid. The illustrative drilling fluid may also include a wide varietyof conventional components of drilling and well bore fluids, such asfluid loss control agents, suspending agents, viscosifying agents,rheology control agents, as well as other compounds and materials thatone of skill in the art would be knowledgeable about.

The claimed subject matter also includes a method of disposing of drillcuttings into a subterranean formation. As should be well known to oneof skill in the art, this involves grinding the drill cuttings, whichhave been previously separated from the recirculating drilling fluid, inthe presence of a fluid to form a slurry. The slurry is then injected byway of a well into a suitable subterranean formation for disposal. Withthis in mind a person of skill should appreciate that one illustrativeembodiment of the claimed subject matter includes: grinding drillcuttings in a water-base fluid to form a slurry, in which the waterbased fluid is formulated to include: an aqueous based continuous phaseand a shale hydration inhibition agent present in sufficientconcentration to substantially reduce the swelling of the shale and theninjecting the slurry into the subterranean formation designated fordisposal of the cuttings. The shale hydration inhibition agent utilizedin the formulation of the fluid is that which is substantive describedabove. That is to say the shale hydration inhibition agent utilized inone embodiment of the illustrative method has the formula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. Alternatively, the shale hydration inhibition agent ofthe illustrative method may be selected from

as well as mixtures of these. As noted above, the illustrative shalehydration inhibition agent is preferably the reaction product of ahydrogenation reaction of the product of the reaction of triethanolamine and acrylonitrile. Alternatively the shale hydration inhibitionagent may be the reaction product of a hydrogenation reaction of theproduct of the reaction of diethanolamine and acrylonitrile. Theillustrative fluid is formulated such that the aqueous based continuousphase may be selected from: fresh water, sea water, brine, mixtures ofwater and water soluble organic compounds as well as mixtures andcombinations of these and similar aqueous based fluids that should beknown to one of skill in the art. In one illustrative embodiment, anoptional viscosifying agent is included in the drilling fluid and theviscosifying agent is preferably selected mixtures and combinations ofcompounds that should be known to one of skill in the art such asxanthan gums, starches, modified starches and synthetic viscosifierssuch as polyarcylamides, and the like. A weighting material such asbarite, calcite, hematite, iron oxide, calcium carbonate, organic andinorganic salts, as well as mixtures and combinations of these andsimilar compounds that should be known to one of skill in the art mayalso be included into the formulation of the illustrative fluid. Theillustrative fluid may optionally include a wide variety of conventionalcomponents of drilling and well bore fluids, such as fluid loss controlagents, suspending agents, viscosifying agents, rheology control agents,as well as other compounds and materials that one of skill in the artwould be knowledgeable about.

It should also be appreciated by one of skill in the art that theclaimed subject matter inherently includes a method of reducing theswelling of shale clay in a well comprising circulating in the well awater-base drilling fluid formulated as is substantially disclosedherein. One such illustrative fluid includes: an aqueous basedcontinuous phase and a shale hydration inhibition agent present insufficient concentration to reduce the swelling of the shale. That is tosay the shale hydration inhibition agent utilized in one embodiment ofthe illustrative method has the formula:

in which A is independently selected from H and CH₂CH₂CH₂NH₂; and inwhich B is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂and CH₂CH₂CH₂NH₂. Alternatively, the shale hydration inhibition agent ofthe illustrative method may be selected from

as well as mixtures of these. As noted above, the illustrative shalehydration inhibition agent is preferably the reaction product of ahydrogenation reaction of the product of the reaction of triethanolamineand acrylonitrile. Alternatively the shale hydration inhibition agentmay be the reaction product of a hydrogenation reaction of the productof the reaction of diethanolamine and acrylonitrile. The illustrativefluid is formulated such that the aqueous based continuous phase may beselected from: fresh water, sea water, brine, mixtures of water andwater soluble organic compounds as well as mixtures and combinations ofthese and similar aqueous based fluids that should be known to one ofskill in the art. In one illustrative embodiment, an optionalviscosifying agent is included in the drilling fluid and theviscosifying agent is preferably selected mixtures and combinations ofcompounds that should be known to one of skill in the art such asxanthan gums, starches, modified starches and synthetic viscosifierssuch as polyarcylamides, and the like. A weighting material such asbarite, calcite, hematite, iron oxide, calcium carbonate, organic andinorganic salts, as well as mixtures and combinations of these andsimilar compounds that should be known to one of skill in the art mayalso be included into the formulation of the illustrative fluid. Theillustrative fluid may optionally include a wide variety of conventionalcomponents of drilling and well bore fluids, such as fluid loss controlagents, suspending agents, viscosifying agents, rheology control agents,as well as other compounds and materials that one of skill in the artwould be knowledgeable about.

While the compositions and methods of this claimed subject matter havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to the processdescribed herein without departing from the concept and scope of theclaimed subject matter. All such similar substitutes and modificationsapparent to those skilled in the art are deemed to be within the scopeand concept of the claimed subject matter as it is set out in thefollowing claims.

1. A composition comprising: an aqueous based continuous phase; aviscosifying agent; and a shale hydration inhibition agent having theformula:

wherein A is independently selected from H and CH₂CH₂CH₂NH₂; and whereinB is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂ andCH₂CH₂CH₂NH₂; and wherein the shale hydration inhibition agent ispresent in sufficient concentration to reduce the swelling of shale. 2.The composition of claim 1 wherein the shale hydration inhibition agentis the reaction product of a hydrogenation reaction of the product ofthe reaction of triethanolamine and acrylonitrile.
 3. The composition ofclaim 1 wherein the shale hydration inhibition agent is the reactionproduct of a hydrogenation reaction of the product of the reaction ofdiethanolamine and acrylonitrile.
 4. The composition of claim 1 whereinthe aqueous based continuous phase is selected from: fresh water, seawater, brine, mixtures of water and water soluble organic compounds andmixtures thereof.
 5. The composition of claim 1 further comprising aweighting material selected from the group consisting of barite,calcite, hematite, iron oxide, calcium carbonate, organic and inorganicsalts, and mixtures thereof.
 6. The composition of claim 1 wherein shalehydration inhibition agent is selected from:

and mixtures of these.
 7. A water-base drilling fluid for use indrilling a subterranean well through one or more subterranean formationscontaining a shale which swells in the presence of water, the drillingfluid comprising: an aqueous based continuous phase; a weighting agent;and a shale hydration inhibition agent having the formula:

wherein A is independently selected from H and CH₂CH₂CH₂NH₂; and whereinB is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂ andCH₂CH₂CH₂NH₂; and wherein the shale hydration inhibition agent ispresent in sufficient concentration to reduce the swelling of the shale.8. The composition of claim 7 wherein the shale hydration inhibitionagent is the reaction product of a hydrogenation reaction of the productof the reaction of triethanolamine and acrylonitrile.
 9. The compositionof claim 7 wherein the shale hydration inhibition agent is the reactionproduct of a hydrogenation reaction of the product of the reaction ofdiethanolamine and acrylonitrile.
 10. The composition of claim 7 whereinthe aqueous based continuous phase is selected from: fresh water, seawater, brine, mixtures of water and water soluble organic compounds andmixtures thereof.
 11. The composition of claim 7 further comprising aviscosifying agent.
 12. The composition of claim 7 wherein the weightingagent is selected from the group consisting of barite, calcite,hematite, iron oxide, calcium carbonate, organic and inorganic salts,and mixtures thereof.
 13. The composition of claim 7 wherein shalehydration inhibition agent is selected from:

and mixtures of these.
 14. A drilling fluid for use in drilling asubterranean well through one or more subterranean formations containinga shale which swells in the presence of water, the fluid comprising: anaqueous based continuous phase; a viscosifying agent and a shalehydration inhibition agent having the formula:

wherein A is independently selected from H and CH₂CH₂CH₂NH₂; and whereinB is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂ andCH₂CH₂CH₂NH₂; and wherein the shale hydration inhibition agent ispresent in sufficient concentration to reduce the swelling of shale. 15.The composition of claim 14 further comprising a weighting materialselected from the group consisting of barite, calcite, hematite, ironoxide, calcium carbonate, organic and inorganic salts, and mixturesthereof.
 16. A fracturing fluid for use in a subterranean well throughone or more subterranean formations containing a shale which swells inthe presence of water, the fluid comprising: an aqueous based continuousphase; a viscosifying agent and a shale hydration inhibition agenthaving the formula:

wherein A is independently selected from H and CH₂CH₂CH₂NH₂; and whereinB is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂ andCH₂CH₂CH₂NH₂; and wherein the shale hydration inhibition agent ispresent in sufficient concentration to reduce the swelling of shale. 17.The composition of claim 16 further comprising a weighting materialselected from the group consisting of barite, calcite, hematite, ironoxide, calcium carbonate, organic and inorganic salts, and mixturesthereof.
 18. A method comprising drilling a subterranean well throughone or more subterranean formations containing a shale which swells inthe presence of water, wherein the drilling is carried out using adrilling fluid including: an aqueous based continuous phase; a weightingagent; and a shale hydration inhibition agent having the formula:

wherein A is independently selected from H and CH₂CH₂CH₂NH₂; and whereinB is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂ andCH₂CH₂CH₂NH₂; and wherein the shale hydration inhibition agent ispresent in sufficient concentration to reduce the swelling of shale. 19.The method of claim 18 wherein the weighting agent is selected from thegroup consisting of barite, calcite, hematite, iron oxide, calciumcarbonate, organic and inorganic salts, and mixtures thereof.
 20. Amethod of reducing the swelling of shale clay in a well comprisingcirculating in the well a water-base drilling fluid comprising: anaqueous based continuous phase and a shale hydration inhibition agenthaving the formula:

wherein A is independently selected from H and CH₂CH₂CH₂NH₂; and whereinB is independently selected from H, CH₂CH₂OH, CH₂CH₂OCH₂CH₂CH₂NH₂ andCH₂CH₂CH₂NH₂; and wherein the shale hydration inhibition agent ispresent in sufficient concentration to reduce the swelling of the shale.21. The method of claim 20 wherein the shale hydration inhibition agentis the reaction product of a hydrogenation reaction of the product ofthe reaction of triethanolamine and acrylonitrile.
 22. The method ofclaim 20 wherein the shale hydration inhibition agent is the reactionproduct of a hydrogenation reaction of the product of the reaction ofdiethanolamine and acrylonitrile.
 23. The method of claim 20 wherein theaqueous based continuous phase is selected from: fresh water, sea water,brine, mixtures of water and water soluble organic compounds andmixtures thereof.